Air-flow sensor for adapter slots in a data processing system

ABSTRACT

An air-flow sensor is configured to be positioned in an air-flow and attached to a surface in a manner that allows air to flow over an extremity of the sensor. The air-flow sensor includes a base plate, a first heater, a first temperature sensor, a spacer, a second heater, a second temperature sensor, and a cap. The base plate is configured to be the coupled to the surface. The first heater is positioned on the base plate and is configured to heat the base plate. The first temperature sensor is positioned to measure a first temperature of the first heater. The spacer is positioned on the first heater and the second heater is positioned on the spacer. The second temperature sensor is positioned to measure a second temperature of the second heater. The cap is positioned on the second heater, which is configured to heat the cap.

BACKGROUND

The disclosure generally relates to a data processing system and, morespecifically, to an air-flow sensor for adapter slots in a dataprocessing system.

In many modern data processing systems (e.g., servers), PeripheralComponent Interconnect Express (PCIe) adapters are placed at a rear ofthe systems, which subjects the adapters to upstream preheat fromprocessors, memory, and other components of the systems. In addition,power levels for adapters have generally risen over time. For example,field-programmable gate array (FPGA) modules routinely dissipate 20 to30 Watts (W). The increased power dissipation and preheat associatedwith other components of a data processing system have made cooling PCIeadapters increasingly challenging.

While processors and memory usually have built-in temperature sensorsthat feed into thermal management algorithms of a data processingsystem, PCIe adapters have been relatively unprotected and rarely haveon-board thermal instrumentation that is accessible by the system. Inaddition, knowledge of the thermal environment (i.e., approaching airspeed and air temperature) to which a given adapter is subjected isoften times more useful for determining supportability or understandingproblems than component temperature alone. Unfortunately, a mechanicallayout of an allocated PCIe area (of a data processing system) usuallyincludes multiple narrow slots and/or pluggable cassettes which are notparticularly suited for the implementation of standard air speedmeasurement techniques, e.g., anemometry or pressure taps.

Even when a temperature of approaching air is known, the temperatureonly represents one piece of information and without additionalinformation (e.g., a speed of the approaching air) diagnosing coolingproblems with PCIe adapters is problematic. Information limited toapproaching air temperature also does not facilitate the implementationof ‘smart servers’ (with internal knowledge of air-flow) that can adjustfan speeds, as needed, according to the adapters that are implemented.

BRIEF SUMMARY

An air-flow sensor is configured to be positioned in an air path andattached to a surface in a manner that allows air to flow over anextremity of the sensor. The sensor includes: a base plate, a firstheater, a first temperature sensor, a spacer, a second heater, a secondtemperature sensor, and a cap. The base plate is configured to becoupled to the surface. The first heater is positioned on the base plateand is configured to heat the base plate. The first temperature sensoris positioned to measure a first temperature of the first heater. Thespacer is positioned on the first heater and the second heater ispositioned on the spacer. The second temperature sensor is positioned tomeasure a second temperature of the second heater. The cap is positionedon the second heater, which is configured to heat the cap.

The above summary contains simplifications, generalizations andomissions of detail and is not intended as a comprehensive descriptionof the claimed subject matter but, rather, is intended to provide abrief overview of some of the functionality associated therewith. Othersystems, methods, functionality, features and advantages of the claimedsubject matter will be or will become apparent to one with skill in theart upon examination of the following figures and detailed writtendescription.

The above as well as additional objectives, features, and advantages ofthe present invention will become apparent in the following detailedwritten description.

BRIEF DESCRIPTION OF THE DRAWINGS

The description of the illustrative embodiments is to be read inconjunction with the accompanying drawings, wherein:

FIG. 1 is a diagram of a relevant portion of an exemplary dataprocessing system environment that includes a data processing systemwith an air-flow sensor, configured according to an embodiment of thepresent disclosure, for an adapter slot of the data processing system;

FIG. 2 is a side view of a relevant portion of an air-flow sensingsystem that includes an air-flow sensor configured according to thepresent disclosure;

FIG. 3 is a top view of the air-flow sensor of FIG. 2;

FIG. 4 is a chart that illustrates an exemplary calibration curve forthe air-flow sensor of FIG. 2; and

FIG. 5 is a flowchart of an exemplary process for obtaining acalibration curve for an air-flow sensor configured according to oneembodiment of the present disclosure.

DETAILED DESCRIPTION

The illustrative embodiments provide an air-flow sensor, a dataprocessing system, and a computer program product (embodied on acomputer-readable storage device) for calibrating an air-flow sensor.

In the following detailed description of exemplary embodiments of theinvention, specific exemplary embodiments in which the invention may bepracticed are described in sufficient detail to enable those skilled inthe art to practice the invention, and it is to be understood that otherembodiments may be utilized and that logical, architectural,programmatic, mechanical, electrical and other changes may be madewithout departing from the spirit or scope of the present invention. Thefollowing detailed description is, therefore, not to be taken in alimiting sense, and the scope of the present invention is defined by theappended claims and equivalents thereof.

It is understood that the use of specific component, device, and/orparameter names are for example only and not meant to imply anylimitations on the invention. The invention may thus be implemented withdifferent nomenclature/terminology utilized to describe thecomponents/devices/parameters herein, without limitation. Each termutilized herein is to be given its broadest interpretation given thecontext in which that term is utilized.

According to various embodiments of the present disclosure, an air-flowsensor that is designed to work within the space confines of an adapter(e.g., PCIe adapter) cassette or slot is disclosed. According to oneaspect, a fixed power is supplied to a first heater or “main heater” ofa sensor to raise a temperature of a top region of the sensor above atemperature of approaching air. In various embodiments, the temperaturerise is measured via one internal temperature sensor and one upstreamexternal temperature sensor (e.g., an internal thermocouple and anupstream thermocouple that is external to the sensor) and is dependanton the speed of the approaching air. In this manner, the measuredtemperature rise can be utilized to determine the speed of the air towhich the sensor is subjected. In addition, a second heater or “guardheater” is implemented in the sensor to prevent conduction heat lossthrough a supporting region to which a base plate of the sensor ismounted. In general, implementation of the guard heater improves theaccuracy of the sensor, as contrasted with so-called ‘heated block’ typeapproaches to measuring air speed. The disclosed sensor can be used tofully characterize a thermal environment within a given adapter (e.g.,PCIe adapter) slot by measuring preheat and air-flow simultaneously.

With reference to FIG. 1, an exemplary data processing environment 100is illustrated that includes a data processing system 110 that includesan adapter slot or cassette 130 (e.g., sized to receive a PCIe adapter)that includes an air generator (e.g., a fan) 136 and an air-flow sensingsystem (i.e., an air-flow sensor 132 and a temperature sensor (e.g.,thermocouple) 134) configured according to one or more embodiments ofthe present disclosure to sense air-flow in an adapter slot and/orcassette. Data processing system 110 may take various forms, such asworkstations, laptop computer systems, notebook computer systems, ordesktop computer systems and/or clusters thereof. Data processing system110 includes a processor 102 (which may include one or more processorcores for executing program code) coupled to a data storage subsystem104, a display 106, one or more input devices 108, and a network adapter109. Data storage subsystem 104 may include, for example, applicationappropriate amounts of various memories (e.g., dynamic random accessmemory (DRAM), static RAM (SRAM), and read-only memory (ROM)), and/orone or more mass storage devices, such as magnetic or optical diskdrives.

Data storage subsystem 104 includes an operating system (OS) 114 fordata processing system 110. Data storage subsystem 104 also includesapplication programs, such as a browser 112 (which may optionallyinclude customized plug-ins to support various client applications), andother applications (e.g., a word processing application, a presentationapplication, and an email application) 118.

Display 106 may be, for example, a cathode ray tube (CRT) or a liquidcrystal display (LCD). Input device(s) 108 of data processing system 110may include, for example, a mouse, a keyboard, haptic devices, and/or atouch screen. Network adapter 109 supports communication of dataprocessing system 110 with one or more wired and/or wireless networksutilizing one or more communication protocols, such as 802.x, HTTP,simple mail transfer protocol (SMTP), etc. Data processing system 110 isshown coupled via one or more wired or wireless networks, such as theInternet 122, to various file servers 124 and various web page servers126 that provide information of interest to the user of data processingsystem 110.

Those of ordinary skill in the art will appreciate that the hardwarecomponents and basic configuration depicted in FIG. 1 may vary. Forexample, the fan may be located within an electronics enclosure but notnecessarily directly associated with the adapter. The illustrativecomponents within data processing system 110 are not intended to beexhaustive, but rather are representative to highlight components thatmay be utilized to implement the present invention. For example, otherdevices/components may be used in addition to or in place of thehardware depicted. The depicted example is not meant to implyarchitectural or other limitations with respect to the presentlydescribed embodiments.

With reference to FIG. 2, a side view of a relevant portion of anexemplary air-flow sensing system 200 is illustrated, as located withinan adapter slot or cassette that includes a bottom wall 202 and a topwall 204. System 200 includes air-flow sensor 132, temperature sensor134, and fan 136. While air-flow sensor 132 is illustrated as beingattached (e.g., using an adhesive 205) to an inner surface of bottomwall 202, it should be appreciated that depending on the applicationair-flow sensor 132 may be mounted to an inner surface of top wall 204or sidewalls (not illustrated) of the adapter slot or cassette. Ingeneral, sensor 132 is configured to be positioned in an air path in amanner that allows air to flow over an extremity of sensor 132.

Air-flow sensor 132 includes a base plate 206, a guard heater 203, afirst temperature sensor 208, a spacer 210, a main heater 213, a secondtemperature sensor 212, and a cap (or top plate) 214. Guard heater 203is positioned on base plate 206 (e.g., using an adhesive (not shown))and is configured to heat base plate 206. First temperature sensor 208,which may be embedded in a thermally conductive material is positionedto measure a first temperature of guard heater 203. Spacer 210 ispositioned on temperature sensor 208 and is made of a low thermalconductivity material (e.g., spacer 210 has a thermal conductivity lessthan about 0.4 Watts per meter Kelvin (W/mK)). Second temperature sensor212, which may be embedded in a thermally conductive material, ispositioned on spacer 210. Main heater 213 is positioned between secondtemperature sensor 212 and cap 214 and is configured to heat cap 214.Alternatively, heaters 203 and 213 may act as electrical resistancethermometers and, in this case, air-flow sensor 132 may be operatedwithout internal temperature sensors 208 and 212.

In one or more embodiments, air-flow sensor 132 is bilaterally orradially symmetric about its central axis extending through the centersof base plate 206, spacer 210, and cap 214. As shown in FIG. 3, in atleast one embodiment, air-flow sensor 132 has a cylindrical shape whenviewed in plan that allows air-flow sensor 132 to be used irrespectiveof the orientation of incoming air-flow. In other embodiments, air-flowsensor 132 may be implemented with a different shape (e.g., a box or acube).

In one or more embodiments, an air-flow sensor 132 includes: a circularmetal (e.g., aluminum) base plate; an electrically powered guard heater(e.g., patterned metal lines (e.g., nickel or tungsten lines) encased ina polymide film such as Kapton®)), a first silicone epoxy or adhesiveinterface layer; a guard heater temperature sensor (e.g., thermocouple)embedded in the first silicone epoxy or adhesive interface layer; apolycarbonate resin thermoplastic (e.g., Lexan®) middle layer; a secondsilicone epoxy or adhesive interface layer; a main heater temperaturesensor (e.g., thermocouple) embedded in the second silicon epoxy oradhesive interface layer; an electrically powered main heater (e.g.,patterned metal lines (e.g., nickel or tungsten lines encased in apolymide film such as Kapton®)), and a circular metal (e.g., aluminum)top plate. In various embodiments, a thickness of the polycarbonateresin thermoplastic (e.g., Lexan®) middle layer is selected such thatthe thickness is large enough to measure a temperature differentialacross the spacer. For example, the spacer may have a thickness of 5 mm.

During calibration in an air-flow of known speed, main heater 213 issupplied with a fixed known power (e.g., 2 to 3 Watts (W)) that raises atemperature of top plate (cap) 214 above that of the approaching airgenerated by fan 136. The temperature of the approaching air is measuredby a third temperature sensor (e.g., thermocouple 134) placed upstreamof air-flow sensor 132. The power of guard heater 203 is then raiseduntil the temperature difference between main heater 213 and guardheater 203 is negligible. As no net temperature difference exists acrosssensor 132, there is no conduction loss from cap 214 (i.e., the‘sensing’ portion) of air-flow sensor 132, and the calibration oftemperature rise versus air speed is independent of the mountingconditions (e.g., the adhesive used to secure air-flow sensor 132 towall 202, the temperature of wall (e.g., PCIe cassette wall) 202, etc.).In general, air-flow sensor 132 provides a relatively large improvementover conventional ‘heated block’ approaches in which the heat loss to asupport through conduction is often simply modeled and can be arelatively large percentage of the power supplied to main heater 213. Inaddition, the structure of air-flow sensor 132 prevents differences insupport conditions between a data processing system (e.g., server)environment and a calibration environment that may introduce an error incalibration results. For example, a symmetric temperature condition ofair-flow sensor 132 may be illustrated by an ICEPAK® computational fluiddynamics software simulation.

With reference to FIG. 4, the above-described measurement procedure isrepeated with a fixed main heater power for various air speeds tofacilitate the construction of a calibration curve 400 for sensor 132.In a typical case, an accuracy of the disclosed air-flow sensor islimited almost entirely by an accuracy of the anemometer used to measurethe air speed during calibration (typically +/−0.33-0.35 m/s), as errorsin thermocouple readings and electrical power dissipation are relativelysmall in comparison. It should be appreciated that enhanced accuracy canbe achieved with improvements in the calibration standard. Followingcalibration, the air-flow sensor and an upstream temperature sensor(e.g., thermocouple) are mounted into an adapter cassette. Using thesame main heater power used during calibration and adjusting the guardheater to achieve the zero temperature difference condition, themeasured temperature rise and calibration curve yield the average airspeed within the adapter cassette.

In one embodiment, proportional-integral-derivative (PID) type automaticadjustment of guard heater power and repeatable fabrication that doesnot require part-by-part calibration can be readily realized to providea ‘smart server’ with accurate knowledge of air-flow in an adapter area.While the discussion herein focuses on a guarded hot plate air-flowsensor designed and calibrated for adapter slots of a data processingsystem, it is contemplated that the sensor can be used for practicallyany fluid flow measurement application for which a calibration schemecan be devised.

With reference to FIG. 5, a flow chart of an exemplary process 500 forcalibrating air-flow sensor 132, according to one embodiment of thepresent disclosure, is illustrated. For example, process 500 may beexecuted by processor 102 of data processing system 110. At block 502,process 500 is initiated (e.g., when a user of data processing system110 initiates a calibration routine) at which point processor 102 causesa fixed known power to be supplied to main heater 213. Next, in block504 processor 102 measures a temperature of approaching air (i.e., airsupplied by fan 136) using air temperature sensor (e.g., thermocouple)134. Then, in block 506, processor 102 causes power supplied to guardheater 203 to be raised until a temperature difference between mainheater 213 and guard heater 203 is negligible (e.g., less than apredetermined value, such as 0.25 degrees Celsius). Next, in block 508,processor 102 determines a temperature rise (i.e., the temperature riseof cap 214 relative to the approaching air). Then, in block 510,processor 102 logs the air speed-temperature pair. Then, in block 512processor 102 determines whether the calibration routine is done (i.e.whether enough calibration points have been determined to provide adesired accuracy). In response to a determination at block 512 that thecalibration routine has completed, control transfers from block 512 toblock 516 where process 500 terminates. In response to a determinationat block 512 that additional calibration points are to be determined,control transfers from block 512 to block 514 where processor 102changes the air speed by controlling fan 136, and control transfers toblock 504. It should be appreciated that air speed may be determined byan anemometer (not shown) or other known technique.

Accordingly, an air-flow sensor has been disclosed herein that includesdual heating elements that facilitate accurate air-flow sensingindependent of how the sensor is mounted or oriented. The disclosedair-flow sensor is particularly advantageous in applications wheresensor orientation is problematic due to packaging constraints orair-flow direction.

In the flow charts above, the methods depicted in FIG. 5 may be embodiedin a computer-readable medium containing computer-readable code suchthat a series of steps are performed when the computer-readable code isexecuted on a computing device. In some implementations, certain stepsof the methods may be combined, performed simultaneously or in adifferent order, or perhaps omitted, without deviating from the spiritand scope of the invention. Thus, while the method steps are describedand illustrated in a particular sequence, use of a specific sequence ofsteps is not meant to imply any limitations on the invention. Changesmay be made with regards to the sequence of steps without departing fromthe spirit or scope of the present invention. Use of a particularsequence is therefore, not to be taken in a limiting sense, and thescope of the present invention is defined only by the appended claims.

As will be appreciated by one skilled in the art, aspects of the presentinvention may be embodied as a system, method or computer programproduct. Accordingly, aspects of the present invention may take the formof an entirely hardware embodiment or an embodiment combining softwareand hardware aspects that may all generally be referred to herein as a“circuit,” “module” or “system.” Furthermore, aspects of the presentinvention may take the form of a computer program product embodied inone or more computer-readable medium(s) having computer-readable programcode embodied thereon.

Any combination of one or more computer-readable medium(s) may beutilized. The computer-readable medium may be a computer-readable signalmedium or a computer-readable storage medium. A computer-readablestorage medium may be, for example, but not limited to, an electronic,magnetic, optical, electromagnetic, infrared, or semiconductor system,apparatus, or device, or any suitable combination of the foregoing, butdoes not include a computer-readable signal medium. More specificexamples (a non-exhaustive list) of the computer-readable storage mediumwould include the following: a portable computer diskette, a hard disk,a random access memory (RAM), a read-only memory (ROM), an erasableprogrammable read-only memory (EPROM or Flash memory), a portablecompact disc read-only memory (CD-ROM), an optical storage device, amagnetic storage device, or any suitable combination of the foregoing.In the context of this document, a computer-readable storage medium maybe any tangible storage medium that can contain, or store a program foruse by or in connection with an instruction execution system, apparatus,or device.

A computer-readable signal medium may include a propagated data signalwith computer-readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including, but not limited to,electromagnetic, optical, or any suitable combination thereof. Acomputer-readable signal medium may be any computer-readable medium thatis not a computer-readable storage medium and that can communicate,propagate, or transport a program for use by or in connection with aninstruction execution system, apparatus, or device. Program codeembodied on a computer-readable signal medium may be transmitted usingany appropriate medium, including but not limited to wireless, wireline,optical fiber cable, RF, etc., or any suitable combination of theforegoing.

Computer program code for carrying out operations for aspects of thepresent invention may be written in any combination of one or moreprogramming languages, including an object oriented programming languagesuch as Java, Smalltalk, C++ or the like and conventional proceduralprogramming languages, such as the “C” programming language or similarprogramming languages. The program code may execute entirely on theuser's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer or entirely on the remote computer or server. In the latterscenario, the remote computer may be connected to the user's computerthrough any type of network, including a local area network (LAN) or awide area network (WAN), or the connection may be made to an externalcomputer (for example, through the Internet using an Internet ServiceProvider).

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems) and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer, specialpurpose computer, or other programmable data processing apparatus toproduce a machine, such that the instructions, which execute via theprocessor of the computer or other programmable data processingapparatus, create means for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

The computer program instructions may also be stored in acomputer-readable storage medium that can direct a computer, otherprogrammable data processing apparatus, or other devices to function ina particular manner, such that the instructions stored in thecomputer-readable medium produce an article of manufacture includinginstructions which implement the function/act specified in the flowchartand/or block diagram block or blocks. The computer program instructionsmay also be loaded onto a computer, other programmable data processingapparatus, or other devices to cause a series of operational steps to beperformed on the computer, other programmable apparatus or other devicesto produce a computer implemented process such that the instructionswhich execute on the computer or other programmable apparatus provideprocesses for implementing the functions/acts specified in the flowchartand/or block diagram block or blocks.

As will be further appreciated, the processes in embodiments of thepresent invention may be implemented using any combination of software,firmware or hardware. As a preparatory step to practicing the inventionin software, the programming code (whether software or firmware) willtypically be stored in one or more machine readable storage mediums suchas fixed (hard) drives, diskettes, optical disks, magnetic tape,semiconductor memories such as ROMs, PROMs, etc., thereby making anarticle of manufacture in accordance with the invention. The article ofmanufacture containing the programming code is used by either executingthe code directly from the storage device, by copying the code from thestorage device into another storage device such as a hard disk, RAM,etc., or by transmitting the code for remote execution usingtransmission type media such as digital and analog communication links.The methods of the invention may be practiced by combining one or moremachine-readable storage devices containing the code according to thepresent invention with appropriate processing hardware to execute thecode contained therein. An apparatus for practicing the invention couldbe one or more processing devices and storage subsystems containing orhaving network access to program(s) coded in accordance with theinvention.

Thus, it is important that while an illustrative embodiment of thepresent invention is described in the context of a fully functionalcomputer (server) system with installed (or executed) software, thoseskilled in the art will appreciate that the software aspects of anillustrative embodiment of the present invention are capable of beingdistributed as a program product in a variety of forms, and that anillustrative embodiment of the present invention applies equallyregardless of the particular type of media used to actually carry outthe distribution.

While the invention has been described with reference to exemplaryembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular system,device or component thereof to the teachings of the invention withoutdeparting from the essential scope thereof. Therefore, it is intendedthat the invention not be limited to the particular embodimentsdisclosed for carrying out this invention, but that the invention willinclude all embodiments falling within the scope of the appended claims.Moreover, the use of the terms first, second, etc. do not denote anyorder or importance, but rather the terms first, second, etc. are usedto distinguish one element from another.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below, if any, areintended to include any structure, material, or act for performing thefunction in combination with other claimed elements as specificallyclaimed. The description of the present invention has been presented forpurposes of illustration and description, but is not intended to beexhaustive or limited to the invention in the form disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the invention.The embodiments were chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

What is claimed is:
 1. A fluid flow sensor configured to be positionedin a fluid flow path and attached to a surface in a manner that allowsfluid to flow over an extremity of the sensor, the sensor comprising: abase plate configured to be the coupled to the surface; a first heaterpositioned on the base plate, wherein the first heater is configured toheat the base plate; a first temperature sensor embedded in a firstthermally conductive material and positioned to measure a firsttemperature of the first heater; a spacer positioned on the firstheater, wherein the first temperature sensor is positioned between thespacer and the first heater and a thickness of the spacer is selected toprovide a measurable temperature differential across the spacer; asecond temperature sensor embedded in a second thermally conductivematerial; a second heater; and a cap positioned on the second heater,wherein the second heater is configured to heat the cap, and wherein thesecond temperature sensor is positioned between the second heater andthe spacer to measure a second temperature of the second heater, wherethe fluid flow sensor has a cylindrical shape that allows the fluid flowsensor to be used irrespective of the orientation of incoming fluid. 2.The sensor of claim 1, wherein the first and second temperature sensorsare thermocouples or calibrated electrical resistanceheaters/thermometers.
 3. The sensor of claim 1, wherein the base plateand cap are made of metal.
 4. The sensor of claim 3, wherein the metalis aluminum.
 5. The sensor of claim 1, wherein the spacer has a thermalconductivity less than about 0.4 Watts per meter Kelvin.
 6. The sensorof claim 5, wherein the spacer is made of a polycarbonate resinthermoplastic.
 7. The sensor of claim 1, wherein the sensor is mountedto the surface with an adhesive.
 8. An air-flow sensing system for anadapter slot, comprising: an air-flow sensor configured to be located inan air path and mounted to a surface in a manner that allows air to flowover an extremity of the air-flow sensor, the air-flow sensor including:a base plate configured to be the coupled to the surface; a first heaterpositioned on the base plate, wherein the first heater is configured toheat the base plate; a first temperature sensor embedded in a firstthermally conductive material and positioned to measure a firsttemperature of the first heater; a spacer positioned on the firstheater, wherein the first temperature sensor is positioned between thespacer and the first heater and a thickness of the spacer is selected toprovide a measurable temperature differential across the spacer; asecond temperature sensor embedded in a second thermally conductivematerial; a second heater; and a cap positioned on the second heater,wherein the second heater is configured to heat the cap, and wherein thesecond temperature sensor is positioned between the second heater andthe spacer to measure a second temperature of the second heater; and athird temperature sensor positioned upstream of the air-flow sensor andconfigured to be located in the air path, wherein the third temperaturesensor is configured to detect a third temperature of air flowing alongthe air path, and wherein the air-flow sensor has a cylindrical shapethat allows the air-flow sensor to be used irrespective of theorientation of incoming air.
 9. The system of claim 8, wherein thefirst, second, and third temperature sensors are thermocouples orcalibrated electrical resistance thermometers.
 10. The system of claim8, wherein the base plate and cap are made of metal.
 11. The system ofclaim 10, wherein the metal is aluminum.
 12. The system of claim 8,wherein the spacer has a thermal conductivity less than about 0.4 Wattsper meter Kelvin.
 13. The system of claim 12, wherein the spacer is madeof polycarbonate resin thermoplastic.
 14. The system of claim 8, whereinthe sensor is mounted to the surface with an adhesive.